1. var maxEnvelopes = function(envelopes) {
    2.     if (envelopes.length === 0) {
    3.         return 0;
    4.     }
    6.     const n = envelopes.length;
    7.     envelopes.sort((e1, e2) => {
    8.         if (e1[0] !== e2[0]) {
    9.             return e1[0] - e2[0];
    10.         } else {
    11.             return e2[1] - e1[1];
    12.         }
    13.     })
    15.     const f = new Array(n).fill(1);
    16.     let ans = 1;
    17.     for (let i = 1; i < n; ++i) {
    18.         for (let j = 0; j < i; ++j) {
    19.             if (envelopes[j][1] < envelopes[i][1]) {
    20.                 f[i] = Math.max(f[i], f[j] + 1);
    21.             }
    22.         }
    23.         ans = Math.max(ans, f[i]);
    24.     }
    25.     return ans;
    26. };
    var maxEnvelopes = function(envelopes) {
    if (envelopes.length === 0) {
        return 0;
    }

    const n = envelopes.length;
    envelopes.sort((e1, e2) => {
        if (e1[0] - e2[0]) {
            return e1[0] - e2[0];
        } else {
            return e2[1] - e1[1];
        }
    })

    const f = [envelopes[0][1]];
    for (let i = 1; i < n; ++i) {
        const num = envelopes[i][1];
        if (num > f[f.length - 1]) {
            f.push(num);
        } else {
            const index = binarySearch(f, num);
            f[index] = num;
        }
    }
    return f.length;
}

const binarySearch = (f, target) => {
    let low = 0, high = f.length - 1;
    while (low < high) {
        const mid = Math.floor((high - low) / 2) + low;
        if (f[mid] < target) {
            low = mid + 1;
        } else {
            high = mid;
        }
    }
    return low;
};